I measured my most recent metal ring. The dimensions get printed ~.5 mm too tight. So the ring CAD would need an offset of .25 mm from the surfaces of the oval that are adjacent to the body and top cap to factor in their print tolerance.
I'm guessing the tightness might come from shrinkage of the metal after casting and cooling. I wonder if they themselves do any compensatory scaling up of the CAD before printing the lost-wax blank?